The key leukocytes associated with chronic inflammation are macrophages. Macrophages play an important role in the development of lung tumors from initiated cells in lung cancer and in experimental respiratory carcinogenesis. We propose a series of in vivo modulations of macrophage activation to determine how these inflammatory phenotypes affect lung tumorigenesis in mouse models. Among the manipulations are exogenous addition of cytokines, bone marrow transplants of genetically distinct marrow populations, varying the number and activation status of pulmonary macrophages during chemical carcinogenesis, as well as using conditional lung-targeted oncogene induction of neoplasia. The macrophage activation states we will examine have distinct physiological roles. M1 activation results from bacterial infection, while M2 activation is key in adaptive immunity. To distinguish between these two phenotypes, we examine arginine metabolism. M1 activation is characterized by inducible nitric oxide synthase expression which results in arginine metabolism to citruline and nitric oxide while M2 activation results in arginase expression leading to polyamine biosynthesis. We will investigate in vitro co-culture models varying lung epithelial and macrophage composition. We will thus deduce which macrophage activation states can modify lung epithelial cell behavior, and examine how epithelial cells at different states of neoplasia affect macrophages. These experiments will provide a molecular understanding of how inflammation promotes lung cancer.